Business data communications 5e by stallings chapter 12

Business Data Communications, 5e2 Switching Techniques • Data transmitted through a network of intermediate switching nodes, which are not concerned with content • End devices receivin

Trang 1

Chapter 12:

Circuit Switching

and Packet Switching

Business Data Communications, 5e

Trang 2

2

Switching Techniques

• Data transmitted through a network of

intermediate switching nodes, which are not

concerned with content

• End devices receiving data are stations;

switching devices are nodes

• A collection of nodes is a communication

network

• A switched communication network routes data

from one station to another through nodes

Trang 3

Switched Network

Characteristics

• Some nodes connect only to other nodes for

switching of data; other nodes have one or more stations attached as well.

• Node-station links are generally dedicated to-point links; ode-node links are usually

point-multiplexed links

• Usually, the network is not fully connected;

however, it is desirable to have more than one

possible path through the network for each pair of

Trang 4

4

Types of Switched Networks

• Two different technologies

– Circuit switching

– Packet switching

• Differ in the way the nodes switch information from one link to another between source and destination

Trang 5

Circuit-Switching Stages

• Circuit establishment

• Data transfer

– point-to-point from endpoints to node

– internal switching/multiplexing among nodes

• Circuit disconnect

Trang 6

6

Circuit Establishment

• Station requests connection from node

• Node determines best route, sends message to next link

• Each subsequent node continues the establishment of a

path

• Once nodes have established connection, test message is

sent to determine if receiver is ready/able to accept

message

Trang 7

Data Transfer

• Point-to-point transfer from source to node

• Internal switching and multiplexed transfer from node to

node

• Point-to-point transfer from node to receiver

• Usually a full-duplex connection throughout

Trang 8

8

Circuit Disconnect

• When transfer is complete, one station initiates

termination

• Signals must be propagated to all nodes used in transit in

order to free up resources

Trang 9

Circuit Switching Characteristics

• Channel capacity is dedicated for the duration of a

connection, even if no data are being transferred

• Once the circuit is established, the network is effectively transparent to the users, resulting in negligible delays

• Developed to handle voice traffic but is now also used for data traffic

Trang 10

10

Circuit Switching Applications

• Public Telephone Network (PSTN)

• Private Branch Exchanges (PBX)

• Private Wide Area Networks (often used to interconnect

PBXs in a single organization)

• Data Switch

Trang 11

Public Switched Telephone

– Carry multiple voice circuits using FDM or synchronous TDM

– Managed by IXCs (inter-exchange carriers)

Trang 12

12

Control Signaling

• Manage the establishment, maintenance, and termination

of signal paths

• Includes signaling from subscriber to network, and

signals within network

• For a large public telecommunications network, a

relatively complex control signaling scheme is required

Trang 13

switches that a call has

ended and the path can be

disconnected

• Telephone ring signal

• Transmission of billing information

• Transmission of equipment and trunk status

information

• Transmission of system failure diagnostic

information

• Control of special equipment (e.g satellite

Trang 14

Trang 15

Supervisory Signals

• Binary character (true/false; on/off)

• Deal with the availability of the called subscriber and of the needed network resources

• Used to determine if a needed resource is available and, if

so, to seize it

• Also used to communicate the status of requested

resources

Trang 16

• Resulting address may be propagated through the

network to support the routing function and to locate and ring the called subscriber's phone

Trang 17

Call Information Signals

• Provide information to the subscriber about the status of a call

• In contrast to internal signals (which are analog or digital electrical messages), these are audible tones that can be heard by the caller or an operator with the proper phone set

Trang 18

18

Network Management Signals

• Used for the maintenance, troubleshooting, and overall operation of the network

• These signals cover a broad scope, and it is this category that will expand most with the increasing complexity of switched networks

Trang 19

In-Channel Signaling

• Traditionally, control signals were carried on the same

channel as the call to which the control signals relate

• Drawbacks

– Information transfer rate limited

– Delay between entering a number and

establishing a connection

Trang 20

20

Common-Channel Signaling

• Control signals are carried over paths completely

independent of the voice channels

• One independent control signal path can carry the signals for a number of subscriber channels (i.e is a “common control channel” for these channels)

Trang 21

Softswitch Architecture

• A general-purpose computer running specialized

software that turns it into a smart phone switch

• Cost significantly less and can provide more

functionality

• Can convert digitized voice bits into packets,

opening transmission options (e.g voice over IP)

• Physical switching function: media gateway (MG)

• Call processing logic: media gateway controller

(MGC)

Trang 22

22

Traditional Circuit Switching

Illustration

Trang 23

Softswitch Architecture

Illustration

Trang 24

24

Packet-Switching Networks

• Developed in 1970s for long-distance data transmission

due to circuit switching limitations

– In user/host data connection the line is often idle, so circuit-switching is inefficient

– Circuit-switching requires both devices to

transmit and receive at the same data rate,

limiting interconnection options

Trang 25

Packet Switching Operation

• Data is broken into packets, each of which can be routed

separately

• Advantages: better line efficiency, signals can always be

routed, prioritization option

• Disadvantages: transmission delay in nodes, variable

delays can cause jitter, extra overhead for packet

addresses

Trang 26

26

Packet Switching Illustration

Trang 27

– preplanned route established for all packets

– similar to circuit switching, but the circuit is not dedicated

Trang 28

28

Packet-Switched Routing

• Adaptive routing changes based on network conditions

• Factors influencing routing are failure and congestion

• Nodes must exchange information on network status

• Tradeoff between quality and amount of overhead

Trang 29

• Status information exchanged among nodes

• Control signals regulate data flow using interface

protocols (usually X.25)

Trang 30

30

WANs for Voice

• Requires very small and nonvariable delays for

natural conversation difficult to provide this with packet-switching

• As a result, the preferred method for voice

transmission is circuit-switching

• Most businesses use public telephone networks,

but some have implemented private voice networks

• VoIP uses packet transmission over Internets and intranets; it is enjoying gradually growing

acceptance as an alternative

Trang 31

WANs for Data

• Public packet-switched networks

• Private packet-switched networks

• Private leased lines

• Public circuit-switched networks

• Private circuit-switched networks (interconnected digital

PBXs)

• ISDN (integrate packet and circuit switching)

Trang 32

– bursty better suited to packet-switching

• Strategic and growth control limited with public

networks

• Reliability greater with packet-switching

• Security greater with private networks

Định dạng
Số trang	32
Dung lượng	308 KB